Since at present handsets need batteries for power supply, they all confront the problem of power consumption. To lower the power consumption of a handset as much as possible, the handset enters into work mode only when necessary. When the handset does not work, it stays in standby mode. The standby mode is classified into network paging reception mode and dormancy mode. Generally, the network paging reception mode takes several milliseconds to tens of milliseconds, while the dormancy mode takes hundreds of milliseconds to several seconds. The power consumption of a handset in work mode is greater than the power consumption of the handset in network paging reception mode, which in turn is greater than the power consumption of the handset in dormancy mode.
To lower the power consumption of a handset, generally the handset will be designed with two clocks, namely a high speed clock for the work mode and the network paging reception mode, and a low speed clock for the dormancy mode. When in work mode or network paging reception mode, a handset can receive clock synchronization information from a base station, and use a phase lock loop within the handset to synchronize a frequency of a high speed clock of the handset to a frequency of the base station, thereby maintaining stable communication between the handset and the base station. When the handset is in dormancy mode, if the low speed clock of the handset is not synchronized to the clock of the base station, the handset begins to receive network paging next time only after it performs clock synchronization. When the handset is in dormancy mode, if it is required that the low speed clock be synchronized to the clock of the base station, the handset has to compute a frequency difference between the low speed clock and the high speed clock, and then adds the frequency difference for compensation to the low speed clock to maintain timing of the handset during dormancy.
FIG. 1 is a time schematic diagram for obtaining a frequency difference between a low speed clock and a clock of a base station in the prior art. When a handset is in work mode or network paging reception mode, it obtains a frequency difference between a low speed clock and a high speed clock. When the handset enters into dormancy mode, it adds the frequency difference for compensation to the low speed clock to maintain timing of the handset.
In practicing the present invention, the inventor finds that, the time used to compute the frequency difference between the low speed clock and the clock of the base station is quite limited, which results in that the frequency difference is not precise enough.